It hasn't been approved yet but that's not really the reason this is happening. Basically AstraZeneca and Pfizer are prioritising some other places that are paying better and trying to charge some EU countries more, because of course they're gonna do that if it makes them profit. The EU is having a major surprised Pikachu face moment. The UK is trying to make sure they get more vaccines than the EU because they want to stick it to the EU, and because there is no viable vaccine that any EU country has produced, the EU has to eat crow. But EU doesn't want to, so they're now threatening to block vaccine exports because "grrrrr these vaccines are MINE!".

The result is that the EU vaccine is much more of a disaster than the US or the UK, and it's not like things are going according to plan there. This would probably be solved if the EU didn't leave it up to a couple of private companies and decided to use public resources to develop vaccines, and/or cooperate with Russia and China too instead of only ordering from the US and UK, but you know how it goes.